Disclosed in the embodiments herein is an improvement in high speed printing utilizing a combination of two cooperative sheet inverters to improve the overall productivity of the printing system. As is well known, sheet inversion properly coordinated and/or collated with the printing sequence is important for duplexing (both sides sheet printing), sheet output collation, finishing, and the like. The system disclosed herein avoids the typical conventional approach of using a much higher paper path (sheet feeding) velocity in a single inverter (which can be as much as twice the normal paper path or process speed of the printer) yet can maintain collation, maintain a proper inter-sheet gap in the sheet path and insure that successively printed sheets do not impact or interfere with one another, even with high speed printing with rapidly successive sheets moving in the paper paths.
With the disclosed embodiments, sequential sheets in the paper path may be alternatingly inverted by the two inverters. Directly sequential sheets need not be inverted in the same inverter. Thus, a much lower speed inverter operation can be employed, providing numerous advantages. For example, with lower speed inverters, less power may be required, acoustic noise may be lower, and system reliability, including reduced sheet jam rates, may be improved. Also, a subsequent sheet need not be delayed for the inversion of a preceding sheet in order to avoid sheet impact or collision, or sheets becoming out of sequential page order in pre-collated printing. Thus, the disclosed dual inverter system embodiments provide opportunities for, improved high speed pre-collated printing productivity without increasing the operating speeds and sheet reversal rates of sheets in the inverter and without requiring an increase in the inter-sheet or inter-pitch gaps between sheets.
By way of background, various types of sheet inverters are known in the art. The following patent disclosures are noted merely by way of a few examples. In particular, there is art on copiers or printers having two sheet inverters in a printer/finisher system where one inverter is in the duplex loop path and the other inverter is in the finisher input or the output path of the copier or printer. Noted, for example, is FIG. 3 of Xerox Corporation U.S. Pat. No. 5,697,040, issued Dec. 9, 1997 to Douglas T. Rabjohns and James S. Stoll. It shows a xerographic printer with both a duplex path sheet inverter and an output path sheet inverter 176. Also, it is known for example from U.S. Pat. No. 5,568,246, issued Oct. 22, 1996 to Paul D. Keller et al, to combine in series two different printing systems into a so-called dual engine printing system. In doing so, the single inverters of each of these print engines provide two inverters, but they are in two separate print engines. Details of other sheet inverters for other reproduction apparatus include, for example, Xerox Corp. U.S. Pat. Nos. 4,986,529 and 5,131,649, and other references cited therein. However, as will be appreciated from the disclosures herein, those systems do not provide the function, result or advantages of the presently disclosed embodiments.
Further by way of technical background, because of the location of the interfaces between the inverter/duplex loop and the rest of the paper path in many printers, the sheet inverter speed, the duplex loop speed, and the exit speed of the printer, often need to be much higher than the process speed. This also imposes difficulties and constraints on the sheet drives, the registration subsystems, etc.
As will be understood by those skilled in the art, the term xe2x80x9cprocess speedxe2x80x9d in some contexts can refers to the sheet velocity related to the printing rate of the system. For example, in xerographic systems the process speed may be the velocity at which the image substrate sheet is fed to, and image-transferred at, the transfer station engagement with the photoreceptor belt or drum, which is running at the process speed. In general, it is desirable to be able run most of the rest of the paper paths of the reproduction apparatus at substantially the same process speed. Otherwise, sheet acceleration or deceleration is required at the sheet velocity transition zones of the paper paths, and spacing problems between sequential sheets may arise. Sheet acceleration in particular can cause slippage, or other problems, with the frictional drive wheel or belt systems typically used for sheet feeding in reproduction apparatus (printers or copiers). As is also well known in the art, there is a xe2x80x9chandoffxe2x80x9d problem in going between a sheet transport or feeder operating at one velocity and the next, or downstream, sheet transport. Other sheet control or registration issues besides slippage can occur, such as rapid nip release of the upstream feed system, or other loss of accurate sheet position control transitioning problems. However, the term xe2x80x9cprocess speedxe2x80x9d as used herein, unless specified otherwise, may more broadly encompass the velocity of the sheets moving in the particular paper path to which the dual inverters are operatively connected. Especially since, for example, it is known to run printer output paths and/or duplex paths at a higher sheet transport velocity than the sheet velocity at image transfer.
In many high volume printer architectures being used at the present day, the sheet inversion system requires that all sheets being inverted be rapidly accelerated from the process speed to a much higher inverter speed as they enter the inverter. That is, to be accelerated in a very short distance from a process or other speed to approximately twice the process speed for movement into the inverter. That is typically followed by rapid deceleration of the sheet in the inverter from that higher speed, and then re-acceleration to that higher speed for exiting from the inverter. In addition to the above-described difficulties, this also imposes more critical sheet timing and registration problems. With the disclosed embodiments, the much slower velocity of the sheet in the inverters greatly reduces these problems.
There is an additional potential advantage in providing two inverters capable of alternatively providing the same function in the same basic sheet path location, with each inverter capable of running independently. If one inverter system fails, or becomes temporarily unusable, the overall reproduction system can still operate at a reduced processing speed, without a total shutdown. For example, if there is a paper jam in one inverter, the machine controller can sense this and automatically slow down the printing rate to approximately half speed, and exclusively utilize the other available inverter until the jam is cleared from the jammed inverter.
The disclosed dual alternate inverter embodiments have additional potential advantages. For example, they may utilize, and even duplicate, otherwise conventional or existing inverters or inverter components. That is, this system may use two of any of various well-known or other types of sheet inverters. It may be incorporated into various types of high-speed reproduction apparatus, or finishers therefor, with little modification. For example, an existing high volume Xerox Corporation DocuTech(copyright) 5090 or DocuTech(copyright) 5390 printer, and their existing high volume finishing systems, such as the Xerox Corporation Model Nos. 4135 or 5090 DocuTech(copyright) finishing systems.
The entrance and exit paths and locations of the dual inverters will, of course, vary depending on the desired application of the system and the reproduction apparatus, as will be explained further herein. For example, the location and configuration of the dual inverters and their input and output paths may be different for application in a sheet output or finisher system, as opposed to utilizing the dual inverter system in a duplex loop return path for second side printing. In either case the dual inverters may optionally be in a separate connecting modular unit from the reproduction apparatus.
The functions of both of those two sheet handling and inversion applications are well known per se to those skilled in the art, and need not be discussed in detail herein. The above-cited U.S. Pat. Nos. 5,131,649 and 4,986,529, for example, also shows that a single inverter may be usable for both the functions of duplex path inversion and/or the sheet output inversion. (However, having more than one sheet in an inverter at a time has other issues, and skipping copying pitches to avoid that reduces printing rate productivity.)
As is also well known in the art, sheet inverters may be used even in simplex (only one side printed) printing in some situations. For example, for inverting simplex sheets printed face up in 1 to N (forward serial) order, so that they can be stacked face down as properly collated sets. Or, alternatively, sheets being printed face down (image sides down) in N to 1 (reverse serial) order being inverted for face up stacking. In some systems, having an odd number of natural sheet path inversions, sheet inversion could even required in a sheet path for second color overprinting of the same side of the sheet. That is, the term xe2x80x9cinverterxe2x80x9d in the art can broadly encompass various systems for avoiding a sheet being turned over, as well as being turned over, and/or reversing the leading edge to trailing edge orientation of the sheet, in the overall sheet path.
A specific feature of the specific embodiments disclosed herein is to provide a high speed reproduction apparatus with a sheet path in which closely sequentially spaced apart printed sheets are fed downstream in said sheet path, said sheet path having an operative connection to a sheet inverter system into which said closely sequentially spaced apart printed sheets in said sheet path are fed to be inverted, the improvement wherein, said sheet inverter system comprises dual inverter system operatively connecting with said sheet path, said dual inverter system comprising two independent but cooperative alternate sheet inverters and a sheet gating control system, said sheet gating control system being programmable and operable to alternately direct alternate said closely sequentially spaced apart printed sheets in said sheet path into said alternate independent sheet inverters.
Further specific features disclosed in the embodiments herein, individually or in combination, include those wherein said closely sequentially spaced apart printed sheets in said sheet path are fed at a process velocity, and wherein both of said two independent but cooperative alternate sheet inverters have internal sheet feeding systems operating at substantially said same process velocity, and/or wherein said two independent but cooperative alternate sheet inverters are connected to operate in parallel with one another relative to said sheet path, and/or wherein said high speed reproduction apparatus has a duplex loop path for returning sheets printed on one side to be printed on their other side, and wherein said two independent but cooperative alternate sheet inverters are alternately connected to form a part of said duplex loop path, and/or wherein said high speed reproduction apparatus has a duplex loop return path for returning sheets printed on one side to be printed on their other side, and wherein said two independent but cooperative alternate sheet inverters have respective sheet entrances connecting with said sheet path via said sheet gating control system at spaced apart positions on said sheet path, and wherein said two independent but cooperative alternate sheet inverters have respective sheet exits connecting to said duplex loop return path in parallel with one another, and/or wherein said high speed reproduction apparatus has a printed sheets output path, and said sheet path is a part of said output path, and/or wherein said sheet path is the output path of said high speed reproduction apparatus, and both of said two independent but cooperative alternate sheet inverters are integral said output path, and/or wherein said two independent but cooperative alternate sheet inverters each have sheet input gates which are spaced apart from one another along said sheet path and which are differently actuated by said sheet gating control system to be alternatingly fed alternate sheets from said sheet path, and/or wherein said two independent but cooperative alternate sheet inverters are respectively located upstream and downstream from one another along said sheet path and on the same side of said sheet path, and/or a method of high speed printing of sheets in a reproduction apparatus so that said sheets are outputted in a pre-collated sequential page order, wherein said printed sheets are being fed through at least one paper path in closely spaced sequential order at a process velocity, and wherein said sheets must be inverted in an inverter system without changing said sequential order of said sheets, the improvement comprising, alternately feeding alternate said sheets being fed through said paper path from said paper path into two alternate sheet inverters comprising said inverter system, sequentially alternately feeding said alternate sheets out of said alternate sheet inverters so as not to change said sequential order of said sheets, and operating both of said alternate sheet inverters at a sheet feeding velocity which is not substantially greater than said process velocity of said paper path, and/or wherein said reproduction apparatus is a duplex printer having a duplex path for feeding said sheets from said paper path for printing their opposite sides, wherein said alternate sheet inverters operatively connect said paper path with said duplex path to provide inversion of said sheets for said printing of their opposite sides, and/or wherein said alternate sheet inverters each have independently operable sheet input gates which are spaced apart from one another along said sheet path and which are differently actuated by a sheet gating control system to be alternatingly fed alternate sheets from said sheet path.
The disclosed system may be operated and controlled by appropriate operation of conventional control systems. It is well-known and preferable to program and execute imaging, printing, paper handling, and other control and logic functions of reproduction apparatus and finishers with software instructions for conventional or general purpose microprocessors, as taught by numerous prior patents and commercial products. Such programming or software may of course vary depending on the particular functions, software type, and microprocessor or other computer system utilized, but will be available to, or readily programmable without undue experimentation from, functional descriptions, such as those provided herein, and/or prior knowledge of functions which are conventional, together with general knowledge in the software or computer arts. Alternatively, a disclosed control system or method may be implemented partially or fully in hardware, using standard logic circuits or single chip VLSI designs.
The term xe2x80x9creproduction apparatusxe2x80x9d or xe2x80x9cprinterxe2x80x9d as used herein broadly encompasses various printers, copiers or multifunction machines or systems, xerographic or otherwise, unless otherwise defined in a claim. The term xe2x80x9csheetxe2x80x9d herein refers to a usually flimsy physical sheet of paper, plastic, or other suitable physical substrate for images, whether precut or web fed. A xe2x80x9ccopy sheetxe2x80x9d may be abbreviated as a xe2x80x9ccopyxe2x80x9d or called a xe2x80x9chardcopyxe2x80x9d. A xe2x80x9cprint jobxe2x80x9d is normally a set of related sheets, usually one or more collated copy sets copied from a set of original document sheets or electronic document page images, from a particular user, or otherwise related. A xe2x80x9csimplexxe2x80x9d document or copy sheet is one having its image and any page number on only one side or face of the sheet, whereas a xe2x80x9cduplexxe2x80x9d document or copy sheet has xe2x80x9cpagesxe2x80x9d, and normally images, on both sides, i.e., each duplex sheet is considered to have two opposing sides or xe2x80x9cpagesxe2x80x9d even though no physical page number may be present.
As to specific components of the subject apparatus or methods, or alternatives therefor, it will be appreciated that, as is normally the case, some such components are known per se in other apparatus or applications which may be additionally or alternatively used herein, including those from art cited herein. All references cited in this specification, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be described herein.